The invention is directed to a hearing aid comprising an input transducer, a processing means for useful signals that has an output stage, and an output transducer. The useful signals can be sampled with a sampling frequency before the output stage and can be converted into data words and can also be processed in time-discrete fashion.
DE-AS 27 16 336, incorporated herein, discloses a hearing aid of the type initially cited. An analog-to-digital converter and a circuit for discrete-time processing of the useful signals converted into digital data words are arranged preceding an output stage and following an input transducer (microphone). A sampling frequency is also provided for the discrete-time signal processing. The sampling frequency is selected no lower than twice the upper limit frequency of the useful signals to be processed.
German Patent 36 16 752, incorporated herein, discloses a hearing aid wherein a discrete-time useful signal processing having a pulse-duration modulation is provided in the output stage, this modulation being formed from analog useful signals with the assistance of a delta signal. The output stage is designed as a switching amplifier and is driven with the pulse-duration-modulated signal.
It has been recognized with the invention that, first, a combination of various discrete-time useful signal processing methods in only one hearing aid can be advantageous and that, second, the required expense for the multiple conversion of the useful signals for different discrete-time processing according to methods that differ from one another is relatively high and already leads to space problems in the relatively small hearing aid from the very outset. In particular, it was recognized with the invention that a conversion of the digitally existing data words into a pulse-duration-modulated signal by way of re-conversion into an analog signal, for example with a digital-to-analog converter, and subsequent conversion into a pulse-duration-modulated signal with a delta signal, also involves relatively great circuit-oriented expense.